Optical communication systems provide wireless data links between computers, disk drives, printers and other devices. Reliable optical communication is critical in applications such as banking or computer assisted flight control, where any data loss may have disastrous consequences. An infrared receiver within the optical communication system converts light signals containing encoded data into electronic waveforms, recovering the encoded data. The ratio of the strongest light signal that the infrared receiver can detect without overloading to the weakest light signal that it can detect is the receiver's dynamic range.
Known infrared receivers using a fixed load resistor have small dynamic ranges. This type of infrared receiver can be optimized to detect weak light signals but is then overloaded by strong light signals. Conversely, the infrared receiver can be designed to handle strong light signals without overloading, but it will not then be sensitive enough to detect weak light signals. A second known infrared receiver uses a clamping diode to prevent the infrared receiver from overloading, but it also has a small dynamic range. Although this second infrared receiver can detect weak light signals, strong light signals are truncated by the clamping diode and the data encoded in the strong light signal may be lost.
In accordance with a preferred embodiment of the present invention, an infrared receiver having a large dynamic range is constructed using a variable input resistance. The variable input resistance changes according to the strength of the light signal. In the presence of weak light signals, the variable input resistance is high, enabling the infrared receiver to detect the weak signals. In the presence of strong light signals, the variable resistance is low, preventing the infrared receiver from overloading. This infrared receiver has a large dynamic range and successfully recovers encoded data from both weak and strong light signals, improving the reliability of the data link in optical communication systems.